[FIXED JENKINS-23568] Be sure to release WorkspaceList.Lease deterministically in a finally block.

changelog.html

@@ -55,6 +55,9 @@ Upcoming changes</a>
 <!-- Record your changes in the trunk here. -->
 <div id="trunk" style="display:none"><!--=TRUNK-BEGIN=-->
 <ul class=image>
+  <li class=bug>
+    Possible unreleased workspace lock if SCM polling fails during setup.
+    (<a href="https://issues.jenkins-ci.org/browse/JENKINS-23568">issue 23568</a>)
   <li class=bug>
     Misleading description of the 'workspace' permission.
     (<a href="https://issues.jenkins-ci.org/browse/JENKINS-20148">issue 20148</a>)

core/src/main/java/hudson/model/AbstractProject.java

@@ -1451,9 +1451,9 @@ public abstract class AbstractProject<P extends AbstractProject<P,R>,R extends A
         // OTOH, if a concurrent build is chosen, the user is willing to create a multiple workspace,
         // so better throughput is achieved over time (modulo the initial cost of creating that many workspaces)
         // by having multiple workspaces
-        WorkspaceList.Lease lease = l.acquire(ws, !concurrentBuild);
         Node node = lb.getBuiltOn();
         Launcher launcher = ws.createLauncher(listener).decorateByEnv(getEnvironment(node,listener));
+        WorkspaceList.Lease lease = l.acquire(ws, !concurrentBuild);
         try {
             listener.getLogger().println("Polling SCM changes on " + node.getSelfLabel().getName());
             LOGGER.fine("Polling SCM changes of " + getName());